Recently, demands for a high-resolution and high-quality image have increased in various fields of applications. As an image has higher resolution and higher quality, an amount of data on the image increases more.
Accordingly, when image data is transferred using media such as existing wired or wireless broadband lines or image data is stored in existing storage media, the information transfer cost and the information storage cost increase.
High-efficiency image compressing techniques can be used to effectively transfer, store, and reproduce information on high-resolution and high-quality images.
Inter prediction and intra prediction can be used to enhance image compression efficiency. In the inter prediction, pixel values of a current picture are predicted with reference to information of other pictures. In the intra prediction, pixel values of a current picture are predicted using an inter-pixel relationship in the same picture.
Various methods for making an image equal to an original image can be applied to a process unit, for example, a block, of a predicted picture. Accordingly, a decoder can decode an image more accurately (more closely to an original image), and an encoder can encode an image to reconstruct the image more accurately.
Therefore, it is necessary to study about how to define process units in a picture, for example, how to define a constraint on process units or a constraint on use of the process units.